Microwave/millimeter-wave integrated circuit

ABSTRACT

A microwave/millimeter-wave integrated circuit realizes stable oscillation by reducing time-base variation in load impedance. This IC connects an oscillator to the input terminal of a lange coupler, and connects to the isolation port of the lange coupler a terminating resistor with resistance equal to the load impedance connected to the output terminals of the lange coupler. This stabilizes load impedance to the oscillator, and reduces variation in the oscillation frequency as a result of changes in load impedance.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a microwave or millimeter-waveintegrated circuit using a semiconductor substrate, commonly known as amicrowave monolithic integrated circuit, and more specifically to anoscillation circuit for generating high frequency signals of microwaveor millimeter-wave band with circuit operation stabilized according toload conditions.

[0003] 2. Description of Related Art

[0004] Oscillators used in sensors and communications devices operatingin the microwave and millimeter-wave bands, referred to below as simplyhigh frequency bands, require a low phase noise characteristic. Phasenoise in an oscillator is variation in the oscillation frequency with aperiod longer than that of the oscillation frequency; low phase noise isindicative of stable oscillator operation. Factors contributing to phasenoise include bias, thermal noise, and modulation caused by nonlinearoperation of active elements.

[0005] Changes in load impedance can also cause the oscillationfrequency of an oscillator to vary, a phenomenon known as pulling. Toavoid problems caused by pulling, variations in load are removed by, forexample, connecting the oscillator to an amplifier connected to multiplestages or to an isolator.

[0006] However, because of the difficulties in manufacturing a resonancecircuit with a Q sufficiently high to assure stable oscillator operationin such high frequency band regions as the millimeter-wave band,oscillators operating in such high frequency bands are subject to evengreater loads.

[0007] It is to be noted that coupling of lange couplers is taught inJapanese Patent Laid-Open Publication Nos.10-242719 and 6-177648, andJapanese Patent Laid-Open Publication 9-46225 teaches a commonphase-locked oscillator (PLO).

SUMMARY OF THE INVENTION

[0008] With consideration for the above noted problem, an object of thepresent invention is to provide a microwave/millimeter-wave integratedcircuit capable of maintaining a stable oscillation operation byreducing time-base variation in load impedance.

[0009] To achieve this object, a microwave/millimeter-wave integratedcircuit according to the present invention comprises an oscillator forgenerating and outputting a high frequency signal in themicrowave/millimeter-wave band, and a lange coupler to an input terminalof which is input the high frequency signal output from the oscillator,and to an isolation terminal of which is connected a terminatingresistance equal to a load impedance connected to an output terminal.

[0010] Preferably, this high frequency wave integrated circuit furthercomprises an amplifier for amplifying and outputting a high frequencysignal output from the lange coupler. In this case the output signalfrom the oscillator can be amplified while also improving the outputcharacteristic.

[0011] Alternatively, a high frequency wave integrated circuit accordingto the present invention comprises an oscillator for generating andoutputting a high frequency signal in the microwave/millimeter-waveband; and a directional coupler having a main signal line to one end ofwhich the high frequency signal from the oscillator is input, and to theother end of which is connected a terminating resistor of apredetermined resistance. In this case a high frequency signal outputfrom the oscillator is input to one end of the main signal line of thedirectional coupler, and a terminating resistor of a specific resistanceis connected to the other end of this main signal line. It is thereforepossible to stabilize the load impedance of the oscillator, reducevariation in the oscillation frequency as a result of variation in loadimpedance, and thereby reduce phase noise.

[0012] This high frequency wave integrated circuit further preferablycomprises an amplifier for amplifying and outputting a high frequencysignal output from a sub-transmission line of the directional coupler.By thus using an amplifier, the output signal from the oscillator can beamplified while also improving the output characteristic.

[0013] A microwave/millimeter-wave integrated circuit for generating andoutputting a high frequency signal in the microwave/millimeter-wave bandaccording to a further aspect of the present invention has an oscillatorfor generating and outputting a high frequency signal in themicrowave/millimeter-wave band; a directional coupler having a mainsignal line to one end of which is input the high frequency signal fromthe oscillator; an amplifier for amplifying and outputting a highfrequency signal input from the oscillator through the main signal lineof the directional coupler, and having a bias input terminal to whichbias is input from an external source; and a phase detecting integratedcircuit for phase detecting a signal reflected from the amplifier inputthrough the sub line of the directional coupler, generating an inversephase signal of which the phase is opposite the detected phase, andoutputting the inverse phase signal to a bias input terminal of theamplifier.

[0014] With this aspect of the invention, a phase detector detects thephase component of the signal reflected from the amplifier and obtainedthrough a directional coupler, and a signal inverting this detectedphase is applied to the bias input terminal of the amplifier. Variationover time in the input impedance of the amplifier is thereforecancelled, change in the load impedance as a result of varying inputimpedance can be suppressed, and phase noise can thus be reduced.

[0015] A microwave/millimeter-wave integrated circuit according to yet afurther aspect of the invention has an oscillator for generating andoutputting a high frequency signal in the microwave/millimeter-waveband; and a phase shifter for shifting a phase of a high frequencysignal output from the oscillator to a predetermined phase setting.

[0016] By thus using a phase shifter to shift the phase of theoscillator output signal so that change in the oscillation frequency isgradual, a microwave/millimeter-wave integrated circuit according tothis aspect of the invention can prevent variation over time in the loadimpedance connected to the phase shifter output, reduce change in theoscillation frequency as a result of varying input impedance, and thusreduce phase noise.

[0017] The predetermined phase to which the phase of the oscillatoroutput signal is shifted is preferably a phase at which frequency changein high frequency signal output from the oscillator is smallest forphase change induced by a load of a particular voltage standing waveratio connected to the output terminal of the phase shifter. It istherefore possible to prevent time-base variation in the load impedanceto the oscillator, reduce change in the oscillation frequency as aresult of varying input impedance, and thus reduce phase noise.

[0018] Other objects and attainments together with a fullerunderstanding of the invention will become apparent and appreciated byreferring to the following description and claims taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a typical circuit diagram of a microwave/millimeter-waveintegrated circuit according to a first preferred embodiment of thepresent invention;

[0020]FIG. 2 is a graph showing the oscillation frequency-phase anglecharacteristic of the microwave/millimeter-wave integrated circuit shownin FIG. 1 under a first set of conditions;

[0021]FIG. 3 is a graph showing the oscillation frequency-phase anglecharacteristic of the microwave/millimeter-wave integrated circuit shownin FIG. 1 under a second set of conditions;

[0022]FIG. 4 is a graph showing the oscillation frequency-phase anglecharacteristic of the microwave/millimeter-wave integrated circuit shownin FIG. 1 under a third set of conditions;

[0023]FIG. 5 is a typical circuit diagram of a microwave/millimeter-waveintegrated circuit according to an alternative version of the firstembodiment shown in FIG. 1;

[0024]FIG. 6 is a typical circuit diagram of a microwave/millimeter-waveintegrated circuit according to a further alternative version of thefirst embodiment shown in FIG. 1;

[0025]FIG. 7 is a typical circuit diagram of a microwave/millimeter-waveintegrated circuit according to a second preferred embodiment of thepresent invention;

[0026]FIG. 8 is a typical circuit diagram of a microwave/millimeter-waveintegrated circuit according to a third preferred embodiment of thepresent invention;

[0027]FIG. 9 is a typical circuit diagram of a microwave/millimeter-waveintegrated circuit according to a fourth preferred embodiment of thepresent invention;

[0028]FIG. 10 is a graph showing the oscillation frequency-phase anglecharacteristic of a conventional oscillation circuit used to describethe operating principle of the microwave/millimeter-wave integratedcircuit shown in FIG. 9.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] The preferred embodiments of the present invention are describedbelow with reference to the accompanying figures.

Embodiment 1

[0030]FIG. 1 is a typical circuit diagram of a microwave/millimeter-waveintegrated circuit 1 according to a first preferred embodiment of thepresent invention. As shown in FIG. 1, this microwave/millimeter-wave IC1 comprises a microwave/millimeter-wave band oscillator 2 for generatingand outputting a microwave/millimeter-wave band signal, a lange coupler3, and a terminating resistor 4 connected to the lange coupler 3. It isto be noted that the resistance of this terminating resistor 4 is equalto the total load impedance connected to first output port 3 a andsecond output port 3 b of microwave/millimeter-wave IC 1, and is assumedin the following description of this exemplary embodiment to be 50Ω.

[0031] Ideally with a microwave/millimeter-wave IC 1 thus comprised halfthe output from oscillator 2 is supplied to first output port 3 a and tosecond output port 3 b. The terminating resistor 4 is also connected tothe isolation port of lange coupler 3, and the load impedance apparentto the oscillator 2 is 50Ω even when there is no output from oscillator2.

[0032]FIG. 2 is a graph showing the oscillation frequency versus phaseangle characteristic of the microwave/millimeter-wave integrated circuitshown in FIG. 1 under a first set of conditions. FIG. 2 morespecifically compares the change in oscillation frequency with a changein phase when the load connected to first output port 3 a and secondoutput port 3 b has a voltage standing wave ratio (VSWR) of 1:1 and1.5:1. Note that FIG. 2 shows results obtained with and without thelange coupler 3. In addition, phase was changed 360 degrees at a VSWR of1.5:1.

[0033] As will be known from FIG. 2, the oscillation frequency ranges290 MHz from 60.54 GHz to 60.25 GHz when there is a 360 degree phasechange and no lange coupler 3, but when the lange coupler 3 is used, theoscillation frequency ranges 30 MHz from 60.41 GHz to 60.44 GHz whenthere is a 360 degree phase change. As this graph shows, variation inthe oscillation frequency due to change in the load impedance can bereduced. That is, because frequency variation is phase noise, theeffects of pulling on phase noise can be reduced when, for example, theinput impedance of an amplifier connected immediately after themicrowave/millimeter-wave IC 1 is fluctuating due to a variable supplyvoltage, for example.

[0034]FIG. 3 and FIG. 4 are similar graphs showing the performance ofthe microwave/millimeter-wave IC 1 shown in FIG. 1 under differentoperating conditions. Note that FIG. 3 compares the change inoscillation frequency with a change in phase when the load connected tofirst output port 3 a and second output port 3 b has a voltage standingwave ratio (VSWR) of 1:1 and 2:1. FIG. 4 likewise compares the change inoscillation frequency when the VSWR of the connected load was 1:1 and3:1. Results in both FIG. 3 and FIG. 4 were obtained with and withoutthe lange coupler 3. Note, further, that phase was changed 360 degreesat a VSWR of 2.0:1 and 3.0:1.

[0035] It will be known from FIG. 3 and FIG. 4 that the effect of thepresent invention reducing phase noise as a result of pulling increasesas the input VSWR increases and deteriorates. For example, when no langecoupler 3 is used and the VSWR is 3.0:1 as shown in FIG. 4, theoscillation frequency changes as much as 800 MHz with a 360 degree phasechange. However, when lange coupler 3 is used with termination providedby terminating resistor 4, the effect on circuits connected after thelange coupler 3 can be reduced, and variation in the oscillationfrequency with a change in load impedance can be suppressed to less than{fraction (1/10)} that when a lange coupler 3 is not used.

[0036] It is alternatively possible to connect to each output of thelange coupler 3 shown in FIG. 1 a buffer amplifier 11 a and 11 b foramplifying the output signal from the oscillator 2. Thus, variation inthe oscillation frequency in response to variation in the inputimpedance as a result of fluctuation in the power supply of bufferamplifier 11 a and 11 b is reduced by the effect of terminating resistor4 connected to the isolation port of the lange coupler 3, thus reducingchange in the oscillation frequency, that is, phase noise, caused byvariation over time in the input impedance of buffer amplifier 11 a and11 b. The output signal from oscillator 2 can also be amplified.

[0037] When two ports are not required for microwave/millimeter-wave IC1 output, it is yet further alternatively possible as shown in FIG. 6 toterminate the second output port 3 b using another terminating resistor4. A device thus comprised achieves the same effects at themicrowave/millimeter-wave IC 1 shown in FIG. 1.

[0038] By connecting the oscillator 2 to the input terminal of a langecoupler 3, and connecting a terminating resistor with resistance equalto the total load impedance connected to the output terminals of thelange coupler 3 to the lange coupler 3 isolation port, amicrowave/millimeter-wave integrated circuit according to the firstembodiment of the present invention described above can thus stabilizethe load impedance of the oscillator 2, and thereby reduce variation inthe oscillation frequency as a result of load impedance change. Phasenoise as a result of load impedance change can therefore also bereduced.

Embodiment 2

[0039] A directional coupler can be used in place of the lange coupler 3used in a microwave/millimeter-wave IC 1 according to the firstembodiment above. A microwave/millimeter-wave IC so comprised isdescribed below as a second preferred embodiment of the presentinvention.

[0040]FIG. 7 is a typical circuit diagram of a microwave/millimeter-waveintegrated circuit according to a second preferred embodiment of thepresent invention. Note that like parts in FIG. 1 and FIG. 7 areidentified by like reference numeral, and further description thereof isomitted below.

[0041] As shown in FIG. 7, this microwave/millimeter-wave IC 20comprises an oscillator 2, a directional coupler 21, a terminatingresistor 22 connected to directional coupler 21, and a buffer amplifier23. The oscillator 2 is connected to one end of main transmission line21 a, and terminating resistor 22 is connected between the other end ofmain line 21 a and ground. An input to buffer amplifier 23 is connectedto one end of sub-transmission line 21 b. The output of buffer amplifier23 is connected to output port 24 of the microwave/millimeter-wave IC20.

[0042] In a microwave/millimeter-wave IC 20 thus comprised, the loadimpedance of the oscillator 2 is determined by terminating resistor 22connected to directional coupler 21. A stable load can be realized bysetting terminating resistor 22 to a specific resistance, such as 50Ω sothat buffer amplifier 23 obtains and then outputs the signal output fromoscillator 2 from one end of sub line 21 b in directional coupler 21.

[0043] As will be known from the above description, by connecting theoscillator 2 to one end of a main line 21 a of a directional coupler 21,and connecting a specific terminating resistance to the other end of themain line 21 a, a microwave/millimeter-wave integrated circuit accordingto this embodiment of the present invention stabilizes the loadimpedance of the oscillator 2, and thereby reduces variation in theoscillation frequency, and thus phase noise, with change in the loadimpedance.

Embodiment 3

[0044] As described above, a microwave/millimeter-wave IC 20 accordingto the above second embodiment of the present invention connects theoscillator 2 to one end of a main line 21 a of a directional coupler 21,and connects a specific terminating resistance to the other end of themain line 21 a. It is alternatively possible as described belowaccording to a third embodiment of the present invention, however, touse a directional coupler without using terminating resistor 22.

[0045]FIG. 8 is a typical circuit diagram of a microwave/millimeter-waveintegrated circuit according to a third preferred embodiment of thepresent invention. Note that like parts in FIG. 1, FIG. 7, and FIG. 8are identified by like reference numeral, and further descriptionthereof is omitted below.

[0046] As shown in FIG. 8, a microwave/millimeter-wave IC 30 accordingto this preferred embodiment of the invention comprises an oscillator 2,directional coupler 21, buffer amplifier 31 connected to directionalcoupler 21, and a phase detecting IC 32 such as a phase-locked loopcircuit for detecting the phase component of a reflected signal frombuffer amplifier 31.

[0047] The oscillator 2 is connected to one end of main transmissionline 21 a. Buffer amplifier 31 is connected between the other end ofmain line 21 a and output port 33.

[0048] An input to phase detecting IC 32 is connected to one end ofsub-transmission line 21 b of directional coupler 21. The output ofphase detecting IC 32 is connected to bias input terminal 31 a of bufferamplifier 31, which has a bias circuit.

[0049] In a microwave/millimeter-wave IC 30 thus comprised, the signalreflection of the oscillator 2 output signal from buffer amplifier 31 isinput through intervening directional coupler 21 to phase detecting IC32. The phase detecting IC 32 then detects the phase of the reflectedsignal to obtain the phase component, and generates and outputs a signalof the inverse phase to bias input terminal 31 a of buffer amplifier 31for superimposition to the bias of buffer amplifier 31. Time-basedvariation in the VSWR of the buffer amplifier 31 is thus cancelled.

[0050] A microwave/millimeter-wave IC according to this third embodimentthus detects the phase component of the signal reflected from bufferamplifier 31 through directional coupler 21, and superimposes a signalof the opposite phase on the bias of buffer amplifier 31, by means ofphase detecting IC 32. This microwave/millimeter-wave IC can thus canceltime-base variation in the input impedance of buffer amplifier 31,thereby suppressing variation in the load impedance resulting from suchvariable impedance and reducing phase noise.

Embodiment 4

[0051] A microwave/millimeter-wave integrated circuit according to afourth preferred embodiment of the present invention is basically amicrowave/millimeter-wave integrated circuit according to the firstembodiment in which the lange coupler 3 is replaced by a phase shifter.

[0052]FIG. 9 shows a microwave/millimeter-wave integrated circuitaccording to this fourth embodiment of the present invention. Note thatlike parts in FIG. 1 and FIG. 9 are identified by like referencenumeral, and further description thereof is omitted below.

[0053] As shown in FIG. 9, this microwave/millimeter-wave integratedcircuit 40 comprises a oscillator 2, phase shifter 41, and bufferamplifier 42. The oscillator 2 is connected through phase shifter 41 toan input to buffer amplifier 42. An output of buffer amplifier 42 isconnected to output port 43 of microwave/millimeter-wave integratedcircuit 40.

[0054]FIG. 10 shows the change in oscillation frequency when a load witha 1.5:1 VSWR is connected without a lange coupler 3 connectedimmediately after the oscillator 2 as shown in FIG. 2. As shown in FIG.10, the change in oscillation frequency to a change in phase is gradualin the areas around a phase angle of −60 degrees and +150 degrees asshown by circles A and B. As a result, the phase of the output signalfrom oscillator 2 is shifted by phase shifter 41 to approximately −60degrees or +150 degrees, and this phase-shifted oscillator output isthen obtained from output port 43 of buffer amplifier 42.

[0055] By thus using a phase shifter 41 to shift the phase of the outputsignal from oscillator 2 to a phase at which the change in oscillationfrequency is gradual, a microwave/millimeter-wave integrated circuitaccording to this preferred embodiment can prevent time-based variationin the load impedance to oscillator 2, including load impedance from thebuffer amplifier 42. This microwave/millimeter-wave integrated circuitthus reduces variation in the oscillation frequency due to change in theload impedance, and thereby reduces phase noise.

[0056] Although the present invention has been described in connectionwith the preferred embodiments thereof with reference to theaccompanying drawings, it is to be noted that various changes andmodifications will be apparent to those skilled in the art. Such changesand modifications are to be understood as included within the scope ofthe present invention as defined by the appended claims, unless theydepart therefrom.

What is claimed is:
 1. A microwave/millimeter-wave integrated circuitfor generating and outputting a high frequency signal in themicrowave/millimeter-wave band, comprising: an oscillator for generatingand outputting a high frequency signal in the microwave/millimeter-waveband; and a lange coupler having an input terminal to which is input thehigh frequency signal output from the oscillator, an output terminal,and an isolation terminal to which is connected a terminating resistanceequal to a load impedance connected to the output terminal.
 2. Themicrowave/millimeter-wave integrated circuit according to claim 1,further comprising an amplifier for amplifying and outputting a highfrequency signal output from the lange coupler.
 3. Amicrowave/millimeter-wave integrated circuit for generating andoutputting a high frequency signal in the microwave/millimeter-waveband, comprising: an oscillator for generating and outputting a highfrequency signal in the microwave/millimeter-wave band; and adirectional coupler having a main signal line to one end of which thehigh frequency signal from the oscillator is input, and to the other endof which is connected a terminating resistor of a predeterminedresistance.
 4. The microwave/millimeter-wave integrated circuitaccording to claim 3, further comprising an amplifier for amplifying andoutputting a high frequency signal output from a sub line of thedirectional coupler.
 5. A microwave/millimeter-wave integrated circuitfor generating and outputting a high frequency signal in themicrowave/millimeter-wave band, comprising: an oscillator for generatingand outputting a high frequency signal in the microwave/millimeter-waveband; a directional coupler having a main signal line to one end ofwhich is input the high frequency signal from the oscillator; anamplifier for amplifying and outputting a high frequency signal inputfrom the oscillator through the main signal line of the directionalcoupler, and having a bias input terminal to which bias is input from anexternal source; and a phase detecting integrated circuit for phasedetecting a signal reflection from the amplifier input through the subline of the directional coupler, generating an inverse phase signal ofwhich the phase is opposite the detected phase, and outputting theinverse phase signal to a bias input terminal of the amplifier.